1. Field of the Invention
The invention relates to methods for producing colored coatings on metal articles or elements, and in particular, to methods of forming coatings on metal articles which can be dyed.
2. Description of the Prior Art
The prior art, as exemplified in U.S. Pat. Nos. 2,042,451, 2,334,000, 2,535,794, 3,544,351, 3,615,894, and 3,647,567, includes a number of processes for producing various coatings, including colored coatings, on metal articles. Presently in the manufacture of textile articles with metal fastener elements, such as slide fasteners with metal sliders, the elements are coated with liquid enamel paints which include pigments selected to produce coatings of the desired color when the paints dry or solidify, while the textile portions of the articles are dyed separately from the metal elements; then the enameled fastener elements are attached to the articles to produce completed color-coordinated articles. The separate enameling of the metal slider elements requires the maintenance of an inventory of numerous different color paints as well as complex general planning to coordinate the production activity of each of the articles to be provided with different color metal fastener elements.
The above U.S. Pat. No. 2,334,000 discloses a particular process wherein metal sliders are coated with a white enamel, assembled on white tapes, and then subjected to a dye process to form a colored slide fastener. There have also been previous attempts to form dyeable metal sliders by coating with a polymer; such coatings have been made from dry powder epoxy coatings and from nylon coatings, dry powder nylon coatings being well known in the prior art. The formation of a suitable dyeable coating on sliders and the dyeing of the coating have generally not been commercially successful; the prior art coatings were unevenly dyed, did not readily pick up colors from dyes, or often resulted in colors from certain dyes which substantially differ from or conflict with the colors produced in the slide fastener tapes. Also, the prior art coatings could not withstand the acid mediums employed in many conventional dye processes, or easily chipped and peeled off and thus could not withstand the handling, such as tumble drying, normally given to garments.
The prior art contains a number of prior art processes utilizing baths, including electrostatically charged powder sprays, of powdered polymer resins, including epoxy resins and nylon resins, for producing polymer films or coatings on metal articles. U.S. Pat. Nos. 3,028,251, 3,058,951, 3,321,438, 3,442,856, 3,506,598, 3,102,823, 3,697,331, and 3,758,633 disclose particular epoxy resins for coatings. The powder resins generally contain pigments, such as titanium dioxide and the like, for producing a coating of a desired color. Some of the polymer coatings, particularly the epoxy coatings, have been known for their adherence, durability, and resistance to chemical attack. However, the required powder bath coating equipment and its limited suitability for being repeatedly and conveniently changed to produce different colored coatings along with the higher cost of materials has prevented any extensive adoption of pigment colored powder bath coatings in coating color matching metal fastener elements for dyed articles.
Dyes in the prior art have been successfully utilized to color a variety of materials including fabrics and, as illustrated in U.S. Pat. No. 2,854,367, phosphate treated metal surfaces. The dyes have been divided into a number of general classes, such as acid dyes, direct dyes, disperse dyes, mordant dyes, fiber reactive dyes, basic dyes, azoic dyes, etc. according to their use or properties. Acid dyes are water-soluble anionic dyes that are applied to nitrogenous fibers such as wool, silk, nylon and modified acrylic fibers, from acid or neutral baths; attachment of color groups to the fiber is attributed at least partly to salt formation between anionic groups in the dyes and cationic groups in the fiber. Active amino groups exhibit a basic nature which has been attributed to their ability to attract and dissociate a proton from H.sub.2 O thus forming a cationic group and a free hydroxyl ion. Direct dyes are also considered to be generally anionic in nature and substantive to cellulosic fibers in the presence of an electrolyte such as salt. Disperse dyes are substantially water-insoluble dyes held in aqueous solution by anionic dispersing agents. The disperse dyes are generally believed to migrate from the dispersion, sometimes with the aid of a carrier, into the fibers where the dyes remain due to their insolubility; in nylon fibers hydrogen bonds between amino groups in disperse dyes and carbonyl groups in the nylon fibers may contribute to fixation. Mordant dyes and azoic dyes generally require the reaction of two components in situ in the fiber to produce an insoluble molecule. Although the prior dyeing art is extensive, the various properties of dyes and their application to various materials is not completely understood.